October 21, 2004
Fescue may affect bulls' reproductive performance
For grazing bulls, being "put out to pasture" may be a figure of speech come all too true.
"When cows eat tall fescue, we know it messes up their ability to conceive or maintain a pregnancy, so it makes sense that it could potentially be messing up the bulls' reproductive performance as well," said Karen L. Jones, an animal biotechnologist at Southern Illinois University Carbondale.
Jones, SIUC animal physiologist Sheryl S. King and former undergraduate student Candis A. McCleary have found that a fungus common in tall fescue, a pasture grass that grows throughout the country, may impair bull semen quality. The three researchers followed six Angus bulls over a two-month period last summer, feeding half the animals a diet of fescue infected by the fungus and the other half a diet of corn and wheat. Results of their study appear in the October issue of the journal The Professional Animal Scientist.
"There has been research on the effect of toxic fescue on cows (including work done by Jones and King), but this is the first time anyone has looked at what happens with bulls," Jones said.
Jones acknowledged the small sample makes it a little more difficult to generalize the study's results. The researchers hope to follow this study with a larger one over a longer period of time.
"One of the things we did to increase the vigor (of the study) was to collect semen from these animals more frequently," Jones said.
"That gave us a better history of each animal followed over time as opposed to a snapshot of a single day where he might have performed poorly."
Twice each week, the researchers analyzed sperm shape and motility (the speed with which sperm swim). Averaged out over the study's 60 days, these measures revealed no differences, regardless of what the bulls ate. But analysis focusing on the last two weeks of the study showed definite change. Sperm from the fescue-fed bulls were less active and most of them had bent tails so they couldn't swim very well.
This could be significant. Because it takes roughly 60 days for cattle sperm to mature, those examined in the first six weeks of the study had been produced and, for the most part, had matured before observation began. Only toward the study's end would sperm affected by a fescue diet during their early development begin to turn up.
Then again, it could just be the weather.
"The differences we saw happened to coincide with a hot spell we had in August," Jones said.
"We therefore can't be sure if they were caused by something in the testes or if we were seeing a heat effect."
Using an infrared thermometer, the researchers also found higher than normal temperatures in the testicular arteries of bulls on the fescue diet, even when the animals' body temperatures were what they should be.
"Sperm are very sensitive to elevated temperatures -- when the testes are hot, the sperm die," Jones said.
In addition, the researchers saw an increased concentration of sperm in the bulls that ate the fescue, an outcome that surprised them.
"We don't think the bulls were making more sperm," Jones said. "We think the accessory sex glands were not functioning correctly as there wasn't as much fluid in the ejaculate."
In light of the results from this small sample size, Jones would like to follow up with a larger study of more animals over a longer period of time. She also would like to add a third group of bulls to such a study, feeding them fescue but then treating them with an experimental drug used in previous SIUC research with grazing cows. In that work, she and King showed this drug could reverse the ill effects of toxic fescue on reproductive abilities.
"The ultimate test, of course, would be to use the sperm to find out if they can actually fertilize an egg," Jones said.
"We froze some of the sperm (collected in this study) -- I have the freezer burns to prove it! -- so we could do further study with in vitro fertilization. All we need is the money."